The present invention relates generally to eddy current inspection probes for inspecting a surface of a manufactured component, and more particularly to a probe having an improved fit with the surface of the component.
Eddy current inspection is commonly used to detect flaws in surfaces of manufactured components such as gas turbine engine components. During this type of inspection, electromagnetic induction is used to induce eddy currents in the component being inspected. An array of coils inside an eddy current probe generates alternating magnetic fields which induce the eddy currents in the component when the probe is moved near the component. When flaws are present in the component, the flow of eddy currents is altered. The altered eddy currents produce changes in a secondary magnetic field which are detected by the array of coils inside the eddy current probe. The array generates an electrical signal in response to the altered secondary magnetic field. The amplitude of the electrical signal is generally proportionate to the size of the flaw. Thus, approximate sizes and general locations of flaws may be determined using eddy current probes.
The array must be kept at a constant distance from the surface of the component being inspected to ensure the amplitude of the electrical signal is proportionate to flaw size. One way of ensuring a constant distance is by sizing and shaping the probe substantially identically to the feature being inspected. For instance, if the surface of an opening in a gas turbine engine disk such as a dovetail slot bottom is being inspected, a probe sized and shaped substantially identically to the opening is used.
Frequently, the probe is made to collapse so it can fit into the opening. These collapsible probes generally have an expandable core inside a flexible covering which holds the array. In the past, the covering was bonded to the core. As a result, the covering stretched and distorted as it expanded. Changes in the probe shape prevented the array from being positioned at a uniform distance from the surface being inspected. Further, due to variations in size and shape of the actual features being inspected, gaps sometimes occurred between the probe and the surface which also prevented the array from being positioned at a uniform distance from the surface being inspected.
Among the several features of the present invention may be noted the provision of an eddy current inspection probe for inspecting a preselected surface at least partially defining an opening in a component. The eddy current inspection probe comprises a core having an exterior surface sized and shaped for receipt within the opening of the component. The core is moveable between a retracted position for inserting the probe into and removing the probe from the opening in the component and an expanded position in which the probe is sized and shaped for at least partially filling the opening and contacting the preselected surface of the component for inspecting the surface. In addition, the probe includes a compliant covering positioned over the exterior surface of the core having an inner face facing the core and an outer face opposite the inner face. The probe also comprises an eddy current array positioned over the outer face of the covering for generating and detecting magnetic fields in the component to inspect the preselected surface of the component. The eddy current array has an outer surface shaped substantially identically to the preselected surface of the component when the core is in the expanded position for maintaining the outer surface of the array a preselected distance from the surface of the component. In addition, the probe includes an element positioned between the exterior surface of the core and the inner face of the covering having a coefficient of friction selected to permit the inner face of the covering to move tangentially with respect to the exterior surface of the core as the core is moved from the retracted position to the expanded position to ensure intimate contact between the probe and the preselected surface of the component being inspected.
In another aspect of the present invention, the outer face of the covering has a central portion and opposite end portions extending longitudinally outward from the central portion and the eddy current array is positioned over the central portion of the outer face of the covering. Further, the probe includes a layered element positioned between the exterior surface of the core and the inner face of the covering. The element has a central portion underlying the central portion of the cover and opposite end portions extending longitudinally outward from the central portion of the element and underlying the respective end portions of the covering. The central portion of the element has a first thickness and each of the end portions of the element has a second thickness less than the first thickness so the central portion of the outer face of the covering and the array are raised above the end portions of the outer face of the covering for easing insertion of the central portion of the covering and the array into the opening and ensuring intimate contact between the probe and the preselected surface of the component being inspected.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.